Pintle valves are well known for use in controlling flow of fluids, and especially gases. For example, the recirculation of a portion of the exhaust stream of an internal combustion engine into the intake manifold thereof is typically accomplished via a pintle valve. Such pintle valves are known to be actuated by linearly-acting solenoids, linear stepper motors, or motor-driven rotary arms. In the past, solenoid-driven and stepper motor-driven valves have predominated in the automotive art. However, motor-driven rotary arm valves are becoming more common at present because of inherently higher force capabilities.
In a solenoid-driven or linear stepper motor-driven valve, the pintle is subjected to actuating forces which are exclusively axial. In a rotary arm-driven valve, however, the pintle is subjected to both axial and radial force vectors over most of the travel path of the arm. It is known that radial vectors can cause unwanted wear of a pintle shaft and/or a seal/bearing, also referred to herein as a seal/bushing. The resultant wear can lead eventually to excessive leakage and non-compliant performance. The condition also robs the valve of efficiency and overall performance and durability.
The condition results primarily because a fixed guiding bearing is typically employed to guide the pintle and facilitate proper seating of the valve head on the valve seat. Typically, the engaged length of contact between the bearing and the shaft is several times the diameter of the shaft. Because radial forces are proportional to such length of engagement, in such an arrangement high radial forces are inevitable. The driving mechanism for radial force generation is the necessary variable offset between the centerlines of the actuator and the pintle shaft, which varies as a function of the angular position of the actuator arm. Such offset is necessary to produce working force and is, therefore, unavoidable.
What is needed in the art is an improved mechanism for rotary arm-actuation of a pintle valve wherein the bearing/shaft wear known in prior art valves is eliminated.
It is a principal object of the present invention to eliminate bearing/shaft wear in arm-actuated pintle valves resulting from parasitic radial forces.